In 2023, there were 87 unhealthy days for ozone and fine particle pollution in Los Angeles. This was slightly lower than the 10-year average of 109 days. By comparison, there were only five days in San Francisco that reached unhealthy for sensitive groups or above on the Air Quality Index (AQI) for ozone and PM2.5 in 2023. That year, there were 822 days with unhealthy air pollution in the U.S.
Fine particle pollution can be produced from a number of sources, including emissions from cars, trucks, power plants, and factories, wildfires, as well as from chemical reactions of other air pollutants. Some of these factors also influence ozone, in addition to weather conditions.
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Airnow. (July 19, 2024). Number of unhealthy days for ozone and fine particle pollution in the United States in 2023, by select city [Graph]. In Statista. Retrieved June 24, 2025, from https://www.statista.com/statistics/1413458/unhealthy-air-pollution-days-us-by-select-city/
Airnow. "Number of unhealthy days for ozone and fine particle pollution in the United States in 2023, by select city." Chart. July 19, 2024. Statista. Accessed June 24, 2025. https://www.statista.com/statistics/1413458/unhealthy-air-pollution-days-us-by-select-city/
Airnow. (2024). Number of unhealthy days for ozone and fine particle pollution in the United States in 2023, by select city. Statista. Statista Inc.. Accessed: June 24, 2025. https://www.statista.com/statistics/1413458/unhealthy-air-pollution-days-us-by-select-city/
Airnow. "Number of Unhealthy Days for Ozone and Fine Particle Pollution in The United States in 2023, by Select City." Statista, Statista Inc., 19 Jul 2024, https://www.statista.com/statistics/1413458/unhealthy-air-pollution-days-us-by-select-city/
Airnow, Number of unhealthy days for ozone and fine particle pollution in the United States in 2023, by select city Statista, https://www.statista.com/statistics/1413458/unhealthy-air-pollution-days-us-by-select-city/ (last visited June 24, 2025)
Number of unhealthy days for ozone and fine particle pollution in the United States in 2023, by select city [Graph], Airnow, July 19, 2024. [Online]. Available: https://www.statista.com/statistics/1413458/unhealthy-air-pollution-days-us-by-select-city/
